Carnegie Institution researchers, along with colleagues from the Lawrence Berkeley National Laboratory (Berkeley Lab), Harvard University and other institutions, used atmospheric methane observations from throughout North American in 2007 and 2008 in order to improve the estimated amount of emissions resulting from agriculture, fossil fuel drilling, oil refineries and other industries, the Washington DC-based nonprofit said in a statement.

“The study found large discrepancies with government estimates in some regions of the United States, particularly the south-central US, where total methane emissions were 2.7 times greater than those reported in most inventories,” the institute explained. It went on to state that oil and gas drilling and processing activities in the region could account for half of that total, making that a source of methane five times higher than the most commonly used estimates.

“This is the first study to quantify methane emissions at regional scales within the continental United States with enough spatial resolution to significantly criticize the official inventories,” added Marc Fischer, head of the California Greenhouse Gas Emissions Measurement Project (CALGEM) at Berkeley Lab. “Even if we made emissions from livestock several times higher than inventory estimates would suggest for the southwest, you still don't get enough to cover what's actually being observed. That's why it looks like oil and gas are likely responsible for a large part of the remainder.”

The study also reported that livestock-created levels of the greenhouse gas could be twice as high as previously believed, and that total methane emissions in the US could be 1.5 times and 1.7 times higher than the totals previously estimated by the EPA and the international Emissions Database for Global Atmospheric Research (EDGAR), respectively.

The difference, the study authors said, is that their methodology focuses on first measuring the atmospheric gases content, then using weather/climate data and statistical analysis to trace it back to regional sources, while the EPA and EDGAR take the opposite approach.

Co-author Anna Michalak of the Carnegie Institution of Science's Department of Global Ecology told USA Today that their findings are “a very clear signal” of the amounts of methane emitted by US industrial firms and other sources.

Likewise, Colm Sweeney, lead scientist for the NOAA Earth System Research Lab Aircraft Program (and not one of the scientists involved in the research), called the results “significant.” He added that the study provides a clearer overall picture, highlights discrepancies between the two different approaches, and demonstrates the need for additional observational outposts.